Edit Mode Transparent Objects
1° Possible cause:

"Limit selection to visible" must be Enabled, if you don't want to see behind faces while in edit mode. You can find the icon in the 3D View bar.





2° Possible cause:

Those are artifacts caused by not appropriate settings of camera's clipping limits for your scene.



This is the "default scene", except from the clipping near limit.



Clipping plane determine the boundary of camera's frustum (which is the portion of space where computations are done). The bigger the boundary , the less precise calculations could be. As the calculation in this case are about visibility, here they comes the strange effects.

It may not seems that your frustum is so big, as in your scene clipping planes seem not to far away from the default settings...but you must consider that in that calculation also global scaling is involved...



The cube is 150mx150m, the near clipping plane is 1mm/0.01=10cm and the far clipping plane is 1000m/0.01=100'000m! The scale of the frustum is not optimal for your geometery. I suggest to lower the value of you far clipping plane.